1. Field of the Invention
The present invention relates to a disk drive and a method of manufacturing a disk drive such as a magnetic disk drive having a disk surface. More particularly, the present invention relates to placing the disk drive in a servo track writer having a dual transducer clock head which writes a pair of clock tracks in the data region of the disk surface, wherein the clock tracks are allowed to be partially overwritten while providing a continuous stream of reference timing information to the servo track writer during the servo writing process.
2. Description of the Prior Art
Hard disk drives store large volumes of data on one or more disks mounted on a spindle assembly. The spindle assembly includes a spindle motor for rotating the disks at a substantially constant angular velocity. Disk drives employ a disk control system for interfacing with a host (e.g., a computer) to control the reading and writing of data on a disk. Each disk includes up to two disk surfaces which are capable of storing data. On each disk surface, user data is stored on concentric circular tracks between an outside diameter and an inside diameter of the disk. Servo systems are employed to maintain alignment of a transducer head with a desired target data track (termed xe2x80x9ctrack followingxe2x80x9d), for reading and writing user data on the disk surface within desired control parameters.
Embedded servo systems use servo data on the same disk surface as user data to provide control signals and information employed in the operation of the servo system. User data on the disk surface is divided into groups of data sectors. Embedded servo information is recorded in servo sectors placed in arcuate, radially continuous wedges between the groups of data sectors. In this regard, servo sectors are commonly referred to as xe2x80x9cservo wedgesxe2x80x9d. For example, a concentric data track may include 60 equally spaced servo sectors with data regions (i.e., a region containing data sectors, groups of data sectors or partial data sectors) located between adjacent pairs of servo sectors.
Each servo sector includes fields containing track identification used in track seeking operations and tracking information used in track following operations. For example, the track identification information may include track number or address and sector number, and the tracking information may include automatic gain control (AGC) and phase lock oscillator information (PLO), timing information (e.g. a servo sync word) and servo burst information for positioning a transducer head over the disk surface. The fields are defined by transitions written on the disk surface in patterns readable by the servo system.
During execution of a command to read or write data to a target data sector on the disk surface, servo information is sampled as the servo sectors pass under the associated transducer head. Sector timing is maintained by detecting a timing field within each servo sector.
During manufacturing of the disk drive a servo track writer is employed for precisely writing servo sectors on a disk surface. Because spindle motor speed variations can cause timing errors during the servo writing process, a timing system is utilized to write servo sectors at precise circumferential locations on the disk surface. A positioning system is utilized for positioning a write head to write servo sectors at precise radial locations on the disk surface. In one known method, the disk drive head disk assembly (HDA) is placed in a servo track writer. The positioning system is utilized for incrementally moving the rotary actuator from the outer diameter of the disk to the inner diameter of the disk while writing servo sectors to the disk (i.e., a servo track or a portion of a servo track). The timing system includes a clock head positioned over one of the surfaces of the disk, for writing a clock track on the disk surface. The clock track is used as a timing reference on the disk surface such that when servo sectors are written on the disk surface, the servo sectors are written at precisely located circumferential positions.
Conventionally, a clock track consists of a single track with a finite or known number of transitions written on the disk surface plus an index mark once per revolution. For example, the index mark may comprise an absence of transitions. The clock track is placed outside of the data area (where servo sectors are written on the disk), and typically is located near the outside edge of the disk. By locating the clock track near the outside edge of the disk, the servo track writer does not overwrite the clock track and thereby destroy timing information which may lead to the servo sectors being incorrectly written on the disk surface. There are known disadvantages associated with locating the clock track near the outer edge of the disk. The clock head used for writing the clock track on the disk is confined to a very small area at the outer edge of the disk. Very tight mechanical tolerances must be observed to correctly place the clock head. If placed incorrectly, the clock head will fall short of the targeted disk area, and the clock head and the disk may be damaged by landing on the chamfer of the disk. If the clock head is inserted too far into the head disk assembly, the clock track may be overwritten, which may stop or interrupt the servo writing process.
Other disadvantages exist in positioning the clock head very close to the outer edge of the disk. The outer edge of the disk is not certified by the manufacturer to retain proper tribology for flying heads. Tests have indicated that particulate counts are the highest at the outside diameter of the disk. The presence of defects at the outside diameter of the disk may require the clock track to be written to the disk many times before it is correct. During writing of the clock track on the disk surface, the clock head may pick up debris from the disk surface and contaminate a subsequent head disk assembly placed on the servo track writer.
The clock track provides timing synchronization pulses to update timing circuitry (such as a phase locked loop). It is known to write a clock track in the data region and coasting (postpone updating) the timing circuitry to allow the circuit to run at a fixed frequency while the clock head is passing over portions of the clock track overwritten by the servo sectors. However, while the timing circuitry is coasting, spindle motor speed variations can cause timing error and thereby imprecise location of servo sectors on the disk surface.
There is therefore an advantage to be realized if the clock track could be located in the cleaner, data portion of the disk surface while maintaining a timing reference to write servo sectors at precise locations on the disk surface.
The invention can be regarded as a method of manufacturing a disk drive having a rotary actuator and a disk. The rotary actuator includes a disk transducer head for reading and writing on the disk. The method includes the steps of placing the disk drive in a servo track writer, the servo track writer including a clock head and means for moving the rotary actuator. The clock head includes an inner transducer and an outer transducer, the inner transducer and the outer transducer being radially spaced apart with respect to the disk. The method includes writing a pair of continuous phase coherent radially spaced-apart clock tracks with the clock head, the clock tracks comprising an outer clock track and an inner clock track wherein the inner clock track is disposed closer to an inner diameter of the disk than the outer clock track. The method further includes reading a reference timing clock from either or both of the inner and outer clock tracks with the clock head. The method includes writing a portion of a servo track during a rotation of the disk with the disk transducer head, synchronized to the reference timing clock, the servo track portion comprising a series of equally spaced apart servo sector portions. Furthermore, the method includes incrementally moving the disk transducer head in an arcuate path towards the inner diameter of the disk.
The steps of reading the reference timing clock, writing a portion of the servo track and incrementally moving the disk transducer head are repeated to write a complete set of servo tracks on the disk. The servo sector portions form interruptions in the inner and outer clock tracks. Adjacent inner and outer clock track interruptions are circumferentially displaced from one another so as to enable a continuous stream of clock pulses to be read by the clock transducer.
The foregoing and other features of the invention are described in detail below and set forth in the appended claims.